1. Field of the Invention
This invention generally relates to fiber conduit reactors/contactors, and specifically relates to processes utilizing such devices to effect extraction of metals and/or metalloids from fluidic streams.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Chemical extraction is desirable for a variety of reasons. In particular, many solids, liquids and gases contain contaminants which may hinder their further use and, thus, extraction of the contaminants is desirable. In addition or alternatively, many solids, liquids and gases contain valuable substances which are desirable to extract. Moreover, waste streams often contain pollutants which do not meet environmental regulations. As such, considerable effort and expense is often undertaken to remove the chemical species from fluidic streams and solids. Examples of chemical species that are often extracted from fluid streams and solids include but are not limited to dyes, acids, bases, phenolics, amines, sulfur compounds, solvents, catalysts, drugs, and heavy metals, etc. As a particular example, hydrodesulfurization is often used to desulfurize petroleum streams contaminated with sulfur containing compounds, but the process is relatively expensive and dangerous as it is conducted at high temperatures and pressures.
One manner of chemical extraction involves dispersions of one fluidic phase in another to generate small droplets with a large surface area where mass transfer and reaction can occur. In cases of solvent extraction, one or more chemical agents are used to break down the components within a substance to enable extraction. Those materials which are more soluble or react more readily to a particular acid or base get separated from the rest. The separated materials are then removed, and the process begins all over again with the introduction of more chemicals to leach out more components. In any case, the time required for solvent extraction can vary widely. In particular, some materials need to be allowed to mix and sit for a long period of time for the components to separate out. Complicating things further is that many of the chemicals used as well as some by-products of solvent extraction are extremely hazardous and must be handled and disposed of with great care.
A common method of recovering metals from ores and concentrates is by leaching with a mineral acid. The leached liquid containing the dissolved metal, known as a pregnant leach solution, is collected and further processed to extract and separate the metals. By way of example, rare earth metals are generally recovered from bastnaesite by leaching the host rock with hydrochloric acid. Uranium can be recovered from uranium-containing host rock by leaching with phosphoric acid. Copper, beryllium, nickel, iron, lead, molybdenum, aluminum, and manganese can be recovered from host rock by leaching with nitric acid. Copper, beryllium, nickel, iron, lead, molybdenum, aluminum, germanium, uranium, gold, silver, cobalt, and manganese can be recovered from host rock by leaching with sulfuric acid or hydrochloric acid. In hydrometallurgy, mineral concentrates are separated into usable oxides and metals through liquid processes, including leaching, extraction, stripping, and precipitation. By these means, the elements are dissolved and purified into leach solutions. The metal or one of its pure compounds (such as an oxide) is then precipitated from the leach solution by chemical or electrolytic means. In stripping, the metal in the organic solution is stripped (extracted) by an acidic solution to form a loaded strip liquor (loaded electrolyte), resulting in a much purer metal solution. If the volume of the strip solution is much smaller than that of the organic solution, metal is also concentrated.
Mining metal compounds is relatively simple, but extracting individual elements from the ore can sometimes be difficult. For example, processing of rare earth elements and metals of the precious metal group and the uranium group as well as many other metals often requires dozens of procedures each resulting in minute changes in the complex stream. In many cases the procedures need to be repeated, and thus, separating and extracting a single metal element, especially one of the heavy metal elements, takes a great deal of time, effort and expertise. Furthermore, the complex metallurgical technologies have taken decades to evolve, and each metal element presents its own unique challenges for separating and extracting. As a result, it can take many years for scientists to crack the geological code and design appropriate metallurgic processes for each metal element stream.
A common method of recovering volatile products from solutions involves distillation of the product from the solution. For instance, alcohols are often produced by fermentation and recovered by energy intensive distillation. Another method of recovering chemicals from aqueous or other production streams involves adsorption and desorption from solids, but such processes are often laborious, expensive, and/or produce undesirable waste. For example, pollutants from effluent air streams are frequently processed using solid adsorbants. Another example is adjusting a fermentation broth containing valuable pharmaceutical product through a series of pH changes, passing it through either a silica or a polymeric chromatography packing, and subsequently using reverse phase column chromatography to produce products from an adsorbent resin. After repeating the process a salt of the product is crystallized with a solvent and the crystals are neutralized and the product is precipitated in an organic solvent such as acetone or alcohol to produce pure product.
An undesirable byproduct of many extraction processes is the formation of a gelatinous emulsion of chemical phases (often organic and aqueous phases) known as crud, gunk, grungies, grumos, or a rag layer. Problems can occur as the amount of crud builds up in the system, particularly hindering a system's ability to reduce operational costs and in cases of excessive crud formation (or poor crud management), crud can also impact production. Since it is difficult to avoid the formation of crud, most operations have systems for removing it. A further disadvantage of the formation of crud is that once it is removed from a system it must be treated so that the solvent used to extract the noted chemical can be recovered. Techniques vary at different operations, but all include some basic physical force used to separate the solid and liquid phases of crud, such as a centrifuge, filter press, or agitated tank. When choosing a treatment method, one has to consider the economics associated with stopping production to remove crud, as opposed to processing the crud while the plant is in operation.
Accordingly, it would be desirable to develop different systems and methods for efficiently and cost-effectively extracting chemicals from fluids and solids, particularly systems and methods of reduced complexity and which minimize waste.